1. Field of the Invention
The present invention relates to a recording/reproduction apparatus for carrying out information recording and/or reproduction to/from a flexible recording disk, a driving method therefor, and a disk cartridge containing the recording disk.
2. Description of the Related Art
Recently, a demand for recording a large amount of digital data arises along with digitization of TV broadcast or such. For example, in a field of an optical disk, one method for improving a recording density is to reduce an optical spot diameter applied for information recording/reproduction. Hereinafter, description is made for an optical disk as a typical example. However, a recording disk applied in a recording/reproduction apparatus to which the present invention is directed is not limited to an optical disk, and any other used in a form of a disk-shaped recording disk such as a phase change memory, a magneto-optical memory, a hologram memory or such may also be applied.
In order to improve a recording density of an optical disk, shortening of a wavelength of light applied for recording/reproduction and also enlargement of a numerical aperture NA are effective. As to the wavelength of light, near infrared light, i.e., 780 nm is applied for a CD (compact disk), and a wavelength in the neighborhood of 650 nm of red light is applied for a DVD (digital versatile disk). Recently, a blue-violet semiconductor laser has been developed, and it is expected that laser light in the neighborhood of 400 nm will be applied for the future.
As to an objective lens, NA is less than 0.5 for CD, while NA on the order of 0.6 is applied for DVD. For the future, a numerical aperture (NA) is required to be further increased to more than 0.7. However, when NA of an objective lens is increased, and also, wavelength of light is shortened, influence of aberration becomes larger when light is condensed. Accordingly, a margin for tilt of an optical disk decreases. Further, since a focal point depth decreases as NA is increased, focus servo accuracy should be increased.
Further, by applying an objective lens having a high NA, a distance between the objective lens and an optical disk is reduced. Therefore, the objective lens may hit the optical disk immediately before focus servo is withdrawn at starting up, which may cause a trouble in a pickup, if axial runout of the optical disk is not controlled properly. Thus, when disk axial runout is large, high density recording may be much obstructed. This is a common problem not only for an optical disk but also for any other disk-shaped recording medium which is rotated when recording/reproduction is carried out.
In order to solve this problem, a recording/reproduction apparatus having a configuration such that a flexible optical disk is rotated in a condition in which the flexible optical disk is made to face a stabilizing member for the purpose of stabilizing axial runout in the optical disk with the use of aerodynamic force has been proposed. U.S. Patent Application Publication No. 2002/0186636 (paten document 1), Japanese Laid-open Patent Application No. 2003-91970 (paten document 2), Japanese Laid-open Patent Application No. 10-308059 (paten document 3) or ‘OPTICAL READOUT OF VIDEODISC, IEEE TRANSACTION ON CONSUMER ELECTRONICS, November 1976, pages 304-308 (non-patent document 1) discloses such a configuration or a configuration of a flexible optical disk.